KfiSUME OF LITERATURE. 73 



about Ogishkie Muncie Lake [bearing Saganaga granite bowlders]. (6) The aniphi- 

 bolite and chloritic slates. (7) Mica schists and alternations of mica schists and 

 syenite. (8) The syenites and granites of Saganaga and Gull lakes [p. 94]. 



Whether the great quartzite and slate formation (No. 1 above) is the 

 same as the highly tilted slate and quartzite formation which passes into 

 the great conglomerate (No. f) above) of Ogishkie Muncie Lake is an open 

 question, although there are several things which indicate that they are 

 the same. They have been treated throughout, however, as different 

 terranes. The following are given as the considerations which appear to 

 support their equivalency : 



[a) Where the horizontal slates approach the sj^enites at the east end of Gunflint 

 Lake there is nothing to be seen of any beds representing the tilted slates. The 

 syenites and their associated schists come on at once, {h) Where the tilted slates 

 and the conglomerates associated with them are traceable from the syenite upward 

 to the gabbro,-as south of Ogishkie Muncie Lake, there is nothing to be seen of any 

 beds like the horizontal black slates of No. 1. (c) The " Gunflint beds" appear to 

 belong to the horizontal slates of the international boundary at Gunflint Lake, but 

 their supposed equivalents at Ogishkie Muncie Lake belong to schistose and tilted 

 slates and conglomerate, [d) Although the horizontal slates and quartzites of the 

 international boundary strike west and southwest across the State, forming one of 

 the most important topographical features of the northern part of the State, and can 

 be followed for many miles as such, yet they are lost entirely in the region of the 

 upper St. Louis, and the tilted slates are the only ones seen where that river cuts 

 the rock at Knife Falls and below, {e) The great gabbro belt which surmounts the 

 horizontal slates along the international boundary, and prevails to the east and south 

 of their line of strike, is seen to pass to the west of Lake Superior at Duluth, and 

 to disappear from sight suddenly between Duluth and Fond du Lac as if its con- 

 tinuance depended on the maintenance of the horizontal formation with which it is 

 associated. ( /) Where the Gunflint beds become a jaspery hematite, as south and 

 east of Vermilion Lake, the structure of the tilted slates passes into the iron ore as 

 if of the same formation [p. 95]. 



1883. 



Irving, R. D. The coiDper-bearing rocks bf Lake Superior. : Mon. U. S. Geol. 

 Survey Vol. V, 1883, 464 pp. , 15 1. , 29 pi. and maps. See also Third Ann. Rept. U. S. 

 Geol. Survey, 1883, pp. 89-188, 15 pi. and maps; Science, Vol. I, 1883, pp. 140, 359, 

 and 422; and Am. Jour. Sci., 3d ser.. Vol. XXVIII, 1884, p. 462, Vol. XXIX, 1885, 

 pp. 67-68, 258-259, 339-340. 



In the above Irving gives a detailed account of the copper-bearing 

 rocks of Lake Superior, and also discusses the relations of this series to the 



